酸雨对毛竹入侵阔叶林缓冲区根系形态及分布格局的影响

Effects of acid rain on root morphology and distribution pattern in the buffer zone of broad-leaved forest invaded by Moso bamboo

为明确亚热带毛竹与阔叶树根系对酸雨的适应策略,于2017—2018年在浙江省杭州临安天目山国家级自然保护区毛竹入侵阔叶林过渡区开展酸雨模拟试验,选取T1(pH=4.0)、T2(pH=2.5)、CK(pH=5.5)3个模拟酸雨梯度,分析不同强度酸雨作用下毛竹与阔叶树的根系变化。结果表明:T1对阔叶树根系形态指标具有显著的抑制作用(P<0.05),导致阔叶树根系的总根长、总表面积、总体积及和细根比根长分别下降了39.9%,39.4%,42.3%和16.2%;T2对毛竹和阔叶树根系指标均有显著的抑制作用(P<0.05),导致毛竹的根系总根长、总表面积、总体积及细根比根长分别下降了41.5%,42.9%,46.4%和15.1%,阔叶树根系分别下降了60.2%,63.3%,61.8%和20.5%。随着酸雨强度的增加,林内根系生物量密度减少,毛竹将更多的根系置于土壤表层。在水平方向上阔叶树根系则随离树距离的增加而逐渐减少,毛竹2—5 mm径级根系生物量在离竹20 cm,离树40 cm和20 cm之间差异显著(P<0.05)。pH、有机质、可溶有机碳、碱解氮、有效磷和速效钾对毛竹的根系可塑性具有显著的影响(P<0.05)。这些结果表明,毛竹在酸雨作用下利用根系形态可塑性实现种群竞争优势。

Acid rain is an important phenomena in global climate change and it can strongly influence forest ecology. Many studies have shown the impacts of acid rain on root morphology, but the results are very different due to the different species and environmental conditions. Till now, the effects of acid rain on the root morphology of Moso bamboo has not been reported. Moso bamboo(Phyllostachys pubscens), an economically important plant, is often cultivated not only for its delicious shoots and versatile culms, but also as an important biomass resource in southern China. However, with its robust growth and strong rhizomes, Moso bamboo populations have been expanding rapidly into adjacent forests. The ability of Moso bamboo plant to respond to competition through root plasticity may be an important trait for the species, but little information is available on how root systems respond to belowground competition during simulated acid rain. To provide baseline information on the morphological plasticity of the response of Moso bamboo roots during the simulated acid rain we continuously mixed Moso bamboo and broad-leaved forest(transition forest). Three gradients of simulated acid rain treatment including pH 2.5, 4.0 and CK(lake water)were designed to determine the effects of the simulated acid rain on root plasticity in transition forest. This study was conducted in a typical transition zone in the TianMu Mountain Nature Reserve, Zhejiang Province, China, where there is ongoing bamboo expansion. Rhizome and root from transition forest was collected by the soil core method to analyze root morphological parameters. The results showed that(1)T1(pH=4.0)treatment significantly inhibited the root system of broad-leaved trees(P<0.05), resulting in 39.9%, 39.4%, 42.3% and 16.2% decrease in total root length, total surface area, total volume, and special root length, respectively. T2(pH=2.5)treatment significantly inhibited the growth of Moso bamboo and broad-leaved trees(P<0.05).(2)In the vertical direction, the root system biomass of Moso bamboo in 0—10 cm soil layer increased from 81.9% of all root biomass in CK to 87.2% in T2. Simultaneously, the root biomass of broad-leaved trees shifted from the upper to lower soil layers. The root system of Moso bamboo managed to place more biomass in upper soil layers when it encountered other trees, allowing it to gain a competitive advantage.(3)In the horizontal direction, the root biomass of Moso bamboo did not significantly decline with an increase in distance from the sample tree, while the root biomasses of broad-leaved trees decreased with the increasing distance from the sample tree. The inhibition of acid rain on root system was independent of horizontal distance.(4)The pH, organic matter, soluble organic carbon, soil respiration rate, available nitrogen, available phosphorous and available potassium had significant effects on root plasticity of Moso bamboo(P<0.05). It can be seen that, under simulated acid rain, the morphological plasticity of Moso bamboo roots is stronger than that of broad-leaved trees, showing an overall trend of accelerating invasion. Moso bamboo would outcompete trees in the belowground environment. It is of great significance to clarify the competitive position of root plasticity under simulated acid rain for forestry management.